Execute command after seconds (without sleep)

How can I run a command after X seconds without sleep. Or with sleep but without the shell just wait for the response of that command?

I used this but it didn't work

sleep 5 ; ls > a.txt

I need to run it in background. I try not to have to run it in a script I try to run ls after 5 seconds, and shell does not just wait for the end of the sleep

Martin

Posted 2013-04-04T17:25:01.620

Reputation: 252

Why does it not work without the shell? Which error do you get? Are you passing it the full path? Do you know which part parses the ; ? – Hennes – 2013-04-04T17:30:57.430

in this way the shell will block 5 seconds and then run the command., the shell to be stalled I do not need that. – Martin – 2013-04-04T17:37:22.387

Then you either need to start it in a script in the background, or in a sub-shell. – Hennes – 2013-04-04T17:39:29.400

Answers

A more concise way of writing what Hennes suggested is

(sleep 5; echo foo) &

Alternatively, if you need more than a few seconds, you could use at. There are three ways of giving a command to at:

Pipe it:

$ echo "ls > a.txt" | at now + 1 min
warning: commands will be executed using /bin/sh
job 3 at Thu Apr  4 20:16:00 2013

Save the command you want to run in a text file, and then pass that file to at:

$ echo "ls > a.txt" > cmd.txt
$ at now + 1 min < cmd.txt
warning: commands will be executed using /bin/sh
job 3 at Thu Apr  4 20:16:00 2013

You can also pass at commands from STDIN:
```
$ at now + 1 min
warning: commands will be executed using /bin/sh
at> ls
```
Then, press CtrlD to exit the at shell. The ls command will be run in one minute.

You can give very precise times in the format of [[CC]YY]MMDDhhmm[.ss], as in

$ at -t 201412182134.12 < script.sh

This will run the script script.sh at 21:34 and 12 seconds on the 18th of December 2014. So, in theory, you could use at to run something five seconds in the future. However, that is kinda like using a tank to swat a fly, and Hennes's suggestion is better.

terdon

Posted 2013-04-04T17:25:01.620

Reputation: 45 216

Is there any way to use at with a delay in seconds? – Fund Monica's Lawsuit – 2019-03-18T03:48:19.543

@NicHartley no. Use a specific time (e.g. at 21:43) if that's what you want, or just do something simple like sleep 4 && command to run command after 4 seconds. – terdon – 2019-03-18T09:19:34.197

I kept messing with $(sleep 5; echo foo) & I am not sure why I thought I needed a $ in front of that, but with my syntax wrong I just posted the longer (and more understandable) version. ( command_for_in_new_shell ) is shorter though. – Hennes – 2013-04-04T19:23:44.850

@Hennes and I blatantly ripped off your very good idea (which I upvoted). All I did was reformat it to be shorter, all credit for the actual thinking bits is yours :). – terdon – 2013-04-05T14:02:33.037

You can work around it by starting a shell or a script in the background.

Example:

/bin/sh -c "sleep 5 ; echo foo" &
[1] 63791
>                               Active shell prompt here

foo                             5 second later output appears.

Hennes

Posted 2013-04-04T17:25:01.620

Reputation: 60 739